The present invention relates generally to control of shock/boundary-layer interactions caused by supersonic airflow, and more particularly to configurations and actuation of flaps used in control of shock/boundary-layer interactions.
Shockwaves are encountered when an aircraft reaches supersonic airspeeds. Such shockwaves exert significant forces on the thin layer of air around the aircraft, a component referred to as the boundary layer. These shockwaves interact with the boundary layer and, during strong interactions, can cause the boundary layer to be degraded, and may also induce high levels of flow separation. These undesired boundary layer interactions accordingly bring about safety, performance, and longevity concerns, especially when the interactions occur inside of engine inlets.
Systems for alleviating such interactions have been developed. These systems bleed air near the boundary layer to suppress shockwave induced flow separation and improve overall flow uniformity. Active transpiration systems require some sort of ducting and/or pumping to bleed the air, which occupies valuable space, and increases the overall weight and cost of the vehicle.
One alternative to boundary layer bleed is to use cavity recirculation. This passive transpiration control method consists of a porous surface and a cavity underneath. The porous surface can be made of holes or slots. During supersonic flight, the changes in pressure will cause air downstream of the shock impingement to flow into the holes, through the cavity and then out through the holes upstream of the impingement. These systems have reduced mechanical complexity and expense compared to the conventional active transpiration systems. However, present models for passive transpiration systems have disadvantages. Transpiration rates are typically insufficient for effective boundary layer control due to the hole aerodynamics. For example, holes or slots that are normal to the surface create a geometry that is significantly less effective than angled holes for bleeding purposes. Further, the holes can yield increased drag at lower Mach speeds or subsonic air flight because of their continuous open state. This potential leads to the same design concerns experienced in needing to determine the location of shock boundary interaction in a particular aircraft so the holes can be limited to that area. Otherwise, drag losses become too significant.
The present invention is directed to an apparatus for controlling shock/boundary-layer interactions created by a supersonic shock on a surface of a structure. The apparatus includes a cavity formed in the structure and having an opening on the surface. A plate is attached to the surface and covers the opening. A plurality of flaps are formed on the plate and is operable to cooperatively close the opening in response to subsonic airflow condition over the flaps, and open the opening to permit airflow through the cavity in response to supersonic airflow conditions over the flaps.